However, a higher ratio of omega-6 to omega-3 actually seemed to increase cancer risk, and experts say it's important to balance the fatty acids in your diet.
Consuming both omega-3 and omega-6 fats -- acids often found in plant-based foods and oily fish -- may affect cancer risk, according to an October study published in the International Journal of Cancer.
The study found that the more omega-3 and omega-6 fats circulating in study participants' blood, the lower their overall likelihood of developing cancer. The association held for 14 different types of cancer, including colon, stomach, lung, brain, bladder, and others.
According to study author Kaixiong "Calvin" Ye, PhD, of the University of Georgia Department of Genetics, these findings confirm what previous studies have hinted. "There have been previous reports about the potential benefits of omega-3 and omega-6 fatty acids in reducing cancer incidence and mortality," he said.
However, he noted that the new research attempted to avoid some of the limitations of earlier studies, such as relying on self-reported data, using small sample sizes, and limiting the number of cancer types examined.
Here's a look at what the new research found specifically, as well as what the study means for diet and cancer risk.
Omega-3 and omega-6 fats are polyunsaturated fats, meaning they have more than one double-carbon bond in their chemical chain. In omega-3s, this bond is located three carbons away from the end of a chain, whereas in omega-6s, it's six carbons away from the end.
While the two fats share many similarities in their chemical structure and biological pathways, they impact health in some unique ways. "Omega-3 fatty acids are known to be more involved in brain development, cognitive function, and cardiovascular health," Ye said. "Omega-6 fatty acids are more involved in immune function and skin health."
Because the body doesn't produce omega-3 and omega-6 fats naturally, you can only obtain them from food. Some of the best sources of omega-3s are oily fish, whereas plant oils, nuts, and seeds are rich in omega-6s.
Many studies have focused on the impact of omega-3s on cancer prevention, but not as many have addressed the effects of omega-6s. The latest study looked at both.
For their analysis, the researchers examined the cancer incidence and blood levels of omega-3 and omega-6 fats in over 250,000 people enrolled in the UK Biobank, a large biomedical database that has been running since 2006.
With an average follow-up period of 12.9 years, the researchers discovered that, of the 250,000 participants enrolled, around 30,000 developed any of 19 "site-specific" cancers (those that occur in specific body parts, such as the colon, lungs, breasts, or pancreas). They then compared these participants' blood samples with that of cancer-free people.
After crunching the numbers, they found that higher omega-3 and omega-6 levels in the blood were associated with a lower risk of multiple cancers. Specifically, elevated levels of omega-3s were linked with a reduced risk of colon, stomach, and lung cancer, while higher omega-6s had a relationship with lower chances of cancers of the brain, bladder, kidney, thyroid, and other body parts.
Some results varied by age, however. "In terms of overall cancer, the protective associations of omega-3 are stronger in the younger age group and in the women," Ye noted. "On the other hand, the protective associations of omega-6 with overall cancer are stronger in the older age group, in the men, and in current smokers."
Other differences showed up between the sexes. Three of the four cancer types that had no link with omega-3 or omega-6 levels were those that affect females -- cancer of the breast, ovary, and uterus. And there was another notable gender-specific outlier: prostate cancer. For reasons unknown, men with higher levels of omega-3s had a higher risk of developing this form of cancer.
The study also showed that a higher ratio of omega-6 to omega-3 was linked with a heightened overall risk of cancer, with the strongest association between the two involved in cancers of the rectum, colon, and lung.
While omega-3 fatty acids have gotten plenty of good press over the years, omega-6s don't have the same shiny reputation. In fact, some social media accounts buzz with anti-omega-6 messaging, saying these fats are inflammatory or promote heart disease. However, public health authorities like the American Heart Association state that omega-6s are good for the heart and even necessary in appropriate amounts.
What appears to be crucial -- for cancer and other health conditions -- is the ratio of omega-3s to omega-6s. "The study shows that, while higher levels of both omega-6 and omega-3 in the blood were linked to a lower cancer risk, [a higher] ratio of omega-6 to omega-3 actually seemed to increase cancer risk," Taylor Janulewicz, RDN, founder of My Cancer Dietitian, told Health. "This suggests that the balance between omega-6 and omega-3 might matter more than we thought." Some research suggests that an omega-6 to omega-3 ratio of 1:1 to 2:1 may be optimal for disease prevention.
If you'd like to add more polyunsaturated fats to your diet, omega-6-rich options include:
And, for more omega-3s, the following foods are a good source:
To boost your intake, Janulewicz recommends starting with food rather than supplements. "Foods offer a range of additional nutrients that support overall health," she said. "Whole foods help the body absorb these nutrients more effectively, while supplements may not offer the same benefits or bioavailability."